1. Field of the Invention
The present invention relates to a phase adjusting system for a carrier chrominance signal, and more particularly to a phase adjuster for a carrier chrominance signal of a composite color television signal of the NTSC or PAL system in which a carrier chrominance signal modulated with chrominance components is superimposed on a luminance signal.
2. Description of the Prior Art
It has been known in the art of processing a television signal to compare a current input signal with an input signal of one frame before thus determining the change of a picture image on a difference signal between those frames and encoding only the changed portions of the picture image in order to reduce the amount of data to be transmitted, and repeating a preceding signal for only the unchanged portions in order to reduce noises, or to record a picture signal of one frame thus producing a still picture therefrom. In those signal processing techniques, when a composite color television signal of the NTSC or PAL system or the like is used, the phase of a chrominance subcarrier signal changes at every horizontal scanning period by 180 degrees in the NTSC system and by 90 degrees in the
system. Accordingly, there exists a phase difference of 180 degrees (in the NTSC system) or 90 degrees (in the PAL system) between a current input signal and an input signal of one frame before. Accordingly, when the change in the picture image is to be detected by the difference signal between those frames, a large difference signal may be produced due to the phase difference of the carrier chrominance signal in spite of the fact that the picture image does not change and the circuit may erroneously determine as if the change or the movement had occurred. Accordingly, it is necessary to use a phase adjusting circuit for a carrier chrominance signal in order to adjust the phases of the carrier chrominance signal between two adjacent frames in order to match the phase of a carrier chrominance signal of one frame before with the phase of a current carrier chrominance signal.
In the past, as will be described in detail with reference to FIG. 1 later as a system for adjusting the phase of a carrier chrominance signal of a composite color television signal, a signal of a scanning line of one horizontal scan period before or after was utilized. In this prior art phase adjusting system for the carrier chrominance signal, when a picture image causes a vertical change of chrominance components or when a luminance signal includes oblique frequency components, a correct carrier chrominance signal was not produced. Accordingly, when the change of the picture image is detected from a difference signal between a current input signal and an input signal of one frame before, there are some instances where the circuit will malfunction. Therefore, the development of a more accurate phase adjuster for the carrier chrominance signal has been desired. Also, in a still picture image reproducing apparatus in which an NTSC system signal of one frame is stored in a frame memory and it is repetitively read out, when one frame of a color television signal is to be constructed by inverting the polarities of the carrier chrominance signals of every other frames by the phase adjuster for a carrier chrominance signal described above, a flicker may appear at an edge of the picture image, for that reason discussed above.